In activated sludge treatment facilities to perform solid-liquid separation of high-concentration activated sludge, an air diffuser disposed in a tankblows out aeration air to supply oxygen to activated sludge in the tank and the organic matter and nitrogen in raw water is treated with the activated sludge, and a mixed liquor in the tank, which is a mixture of water treated and the activated sludge, is subjected to solid-liquid separation by a membrane separator immersed in an aeration tank.
The above membrane separator has a plurality of filtration membrane cartridges and filters a mixed liquid by using a head within the tank as a driving pressure. The air diffuser is disposed beneath the membrane separator and blows out aeration air upwardly. Updraft caused by air lift action of the bubbles of the aeration air flows along the membrane surfaces of filtration membrane cartridges to clean these membrane surfaces. This cleaning suppresses a reduction in the separation function of the filtration membrane cartridges, thereby preventing the membrane separator from resulting in malfunction.
In the above filtration membrane cartridge, a filtration membrane composed of an organic flat membrane, such as ultrafiltration membrane or microfiltration membrane, is provided on the surface of a filter plate and the periphery of the filtration membrane is secured to the filter plate by welding. Its lifetime is generally between two and five years. When this filtration membrane cartridge is put into service, however, its periphery is flapped by updraft to deteriorate the strength of a welded part, which may result in a shorter lifetime than the normal lifetime as described. On the other hand, filtration membranes used in the filtration membrane cartridges are prepared by coating an organic macromolecular membrane material on both sides of a non-woven fabric serving as a substrate. Since such filtration membranes have durability, little or no breakage takes place, however, contamination due to activated sludge progresses with age, leading to a reduction in flux.
Accordingly, it is a primary object of the invention to provide method and apparatus of regenerating filtration membrane cartridges for activated sludge which effect recovery of the filtration function of contaminated filtration membrane cartridges, remedy of broken parts, and replacement of filtration membranes, with ease and at low cost.